The numbers are fudged to be sure - especially if you're counting "peak publishers" where they double/triple count publishers (usually in august) who are hounded into turning in time for past months that they "forgot" to turn in. Probably a lot of these are 1-hour slips that are either fabricated by the publisher or by the elders to avoid getting the 3rd degree from the CO.
There are lots of folks here who talk about turning in fake time, or their group overseer turning in fake time on their behalf. I'm sure it's not an isolated occurrence. Plus when you consider that they can count time for working construction or for "studying" with children (which is often just saying "look at this pretty bug that jehovah made" a few times a day) or counting 15 minutes for people in a nursing home because their kid put a magazine on their lap and wheeled them around. They're definitely below 8 million active JWs.
If you want to exclude active JWs that no longer believe but are stuck in the cult, there's another group that's probably not an insignificant size.